need help with a script that should replace last x digits of a number with "x", it does all but the last x

I have the function attached that takes a string (card number) and should turn the last x digits into "x" to obscure the number. It almost works but turns the last x into "x", it should be everything BUT the last x.

I imagine that there are some, like me, who require a way of getting currency exchange rates for implementation in web project from time to time, so I thought I would share a solution that I have developed for this purpose.
It turns out that Yaho…